Three-phase compensator



Feb. 11 1941. '1 L. FOUNTAIN 2,231,711

THREE-PHASE COMPENSATOR Eiled D60. 28, 1959 3 x2 ATTORNEY Meade-leali.im

UNITED STATES PATENT OFFICE to Westinghouse Electric & ManufacturingCompanyl -East Pittslnirglnf-A Pa., a.; corporation:

of Pennsylvania Application December 28, 1939, Serial No. 311,394

7 Claims.

vices and has particular relation to means for compensating such devicesconnected to be responsive to a polyphase circuit voltage.

It is frequently desirous to energize a voltage responsive device inaccordance with the average of the three-phase voltages of a threephasecircuit. It is then necessary that the compensating equipment compensatefor the average voltage drop in the three phases of the circuit ifaccurate compensation is to be effected.

Such compensation may be secured by connecting a compensator deviceconsisting of a reactor element and a resistor element into each phaseconductor of the circuit through which the voltage responsive device isenergized and in energizing the several compensator devices withcurrents that bear a predetermined relation to the current iiowing inthe associated phases of the electrical circuit to be compensated. Thecompensators are so connected in the circuit and so adjusted that ohmicand reactive voltage drops across each compensator are proportional tothe ohmic and reactive drops in the associated phases of the circuit. Inacompensator of this character, it has been necessary to employ threeinterconnected' current transformers to secure the necessary shift inthe phase posi- 0 `tion of the current that energizes each compensatorfrom the current flowing in one conductor oi'the associated phase, onetransformer being connected in each conductor of the threelphasecircuit.

In order to avoid the somewhat complicated arrangement of circuits andapparatus required in such compensators, compensating apparatus has beendeveloped for using a single phase voltage produced from one of thephases of the inviti-phase circuit. When a single phase voltage isdeveloped from a single phase current for compensating purposes and isadded or subtracted from a three-phase voltage, the result is anunbalanced three-phase voltage. When such an unbalanced voltage isrectified and applied to the coil of a voltage responsive device, suchas a voltage regulator, the (iO-cycle ripple present in the rectiedvoltage causes the movable element of the regulating device to vibratein unison with it. This vibration is objectionable as effecting thedesired operation of the regulator. Furthermore, such single phasecompensation does not give mathematically true results, and when largevalues of compensating voltages are required, the resulting errorbecomes quite pronounced.

It is an object of my invention to provide a balanced three-phasecompensating voltage from a single-phase current which can be added to,or subtracted from, the three-phase voltage supplied to the controlelement of a voltage regulator or to similar voltage responsive devices.

Other objects and advantages of the invention will be apparent from thefollowing description of one preferred embodiment of the invention,reference being had to the accompanying drawing, in which:

Figure 1 is'a diagrammatic view of circuits and apparatus illustratingan embodiment of the invention; and

Fig. 2 is a vector diagram illustrating the vector relation of thevoltage applied across parts of the apparatus.

Referring to the drawing, a three-phase power circuit is illustratedrepresented by the threephase conductors I, 2 and 3 that are suppliedwith energy from an alternating current generator I, having an armaturewinding 5 connectedr to the three-phase circuit and a. eld winding Iithat is supplied with current from an exciter generator 'I having anarmature Winding 8 and a field winding 9. For the purpose of controllingthe output voltage of the generator 4 a rheostat I2 is provided in thecircuit between the exciter generator 'i and the iield winding 3 havinga movable contact arm I3 actuated through suitable gearing mechanism I4in accordance with the operation of a pilot motor I5 as controlled by aregulator I6. The regulator I6 comprises a Winding Il for magnetizing acore member i8 for varying the position of a regulator lever IS that ispivotally mounted at ZI to actuate a movable contact member 22 intoengagement with the one or the other of the contact members 23 or 24 forcompleting the one or the other of two motor circuits. The motorcircuits extend from a source of electric energy represented by thebattery 25 through the conductor 26, the contact member 22, one of thecontact members 23 or 24, one of the associated conductors 26 or 2l,through the one or the other of the diii'erentially related eld windings28 or 29. the armature winding 32 and the conductor 33 to the battery 25to operate the motor I5 in the one or the other direction. The regulatorwinding I`I is supplied with energy from` three rectifier units 34, 35and 36 each consisting of a pair of rectifier elements between which oneconductor of a three-phase circuit is connected. The three conductors ofthe local circuit supplying the rectifier units are identified as I', 2'andv 3 to correspond, re-

speetively, with the conductors I, 2 and 3 of the 5 power circuit towhich they are connected through transformers 31 and 33. The threephasevoltage impressed on the local circuit conductors I, 2' and 3 by thetransformers 31 and 38, is a measure of the three-phase voltage of thepower circuit and is represented in the vector diagram of Fig. ,2 by thethree solid vector lines I-2, 2-3, and 3I. The current in the threeconductors I, 2 and 3 is represented by the three vectors Ir, Iz, andI1, respectively, at 100% P. F. load.

Two compensating device 42 and 43 are provided for the purpose ofintroducing voltage components into the local circuit such that thethree-phase voltage impressed on the rectiflers 34, 35 and 36 foractuating the voltage responsive device I6 will correspond to thevoltage of the power circuit I. 2, 3 at some chosen point in thetransmission line remote from the generator 4. The device 42 is aresistance drop compensator and the device 43 is a reactive dropcompensator. The compensators 42 and 43 are provided withauto-transformer windings 44 and 45, respectively, that are connected ina circuit energized from the current transformer 43 that is associatedwith the phase conductor 3 of the POWer circuit. This circuit extendsfrom one terminal of the transformer 43 through conductor 41 to thecompensator terminal 43 through a variable tap connection 49 to a pointon the winding 44, through a variable tap connection 52, compensatorterminal 53, conductor 54, compensator terminal 55, variable tapconnection 53 to a point on the winding 45, the variable tap connection51, terminal El, and conductor l! to 40 the other side of the currenttransformer 43.

The variable connecting elements 43, 52, 55 and 51 are so adjusted as toimpress desired voltages across the compensator windings 44 and 45.

Referring to the resistance compensator 42, a 45 network including areactor 62, a reactor 33, and

a resistor 64 are connected in series circuit relation to each otheracross the terminals of the winding 44. A voltage Ex that is inquadrature with the voltage impressed on the winding 44 50 is developedacross the reactor 62 and is introduced through transformer 65 into thecircuit through conductor I', the output circuit from the transformer 65being connected to the local circuit conductor I through terminals Xiand 55 Y1. This vector is shown in the diagram of Fig.

2 as in phase with the phase voltage vector I-2 which is in quadraturewith the current vector Ia, representing the current in conductor 3 ofthe main power circuit. The voltage Enis de- 60 veloped across thereactor 53 that is in quadrature with the voltage impressed across thewinding 44 and is introduced through the transformer 66 into the circuitthrough conductor 3. A

voltage Eniis developed across the resistor 54 65 that is in phase withthe voltage impressed across the winding 44 and this voltage componentis introduced into the circuit of conductor 3 through the transformer31. The output windings of the transformers 65 and 81 are con 70 nectedin series with the circuit conductor 3' between the compensatorterminals Xa and Y1.

The resultant voltage Eza is in phase with the voltage vector 3 2, asshown in Fig. 2. 'I'he three voltage vectors En, Em and Eza are shown atthe lower right hand corner in Fig. 2 and are effective to introduce acountervoltage to shorten the main vector 2-3 to the same extent as thevoltage Ex shortens the main vector I-2. Thus if the points Xi and Y: onthe vector diagram of Fig. 2 are connected, a balanced three-phasevoltage results, this voltage being a three-phase voltage compensatedfor ohmic line drop only.

Referring to the reactive drop compensator 43, a network comprising areactor 1I, a resistor 12 and a resistor 13 is connected in seriescircuit relation across the terminals of the winding 45. 'I'he reactor1I develops a voltage component En that is 90 out of phase with thecurrent vector IJ. The resistor 12 'develops a voltage Enx that is inphase with the current vector IJ. These two voltages combine to producethe resultant voltage En that is introduced through the transformer 14between the compensator terminals X1, Y: into the conductor 3'. Thisvector is at right angles tothe phase voltage vector 2-3 as shown inFig. 2.. A voltage En that is in phase with the vector IJ, is developedacross the resistor 13 and impressed through the transformer 15 acrossthe compensator terminals X4, Y; and introduced into the circuit ofconductor 3.y ,This vector, as shown in Fig. 2, is added vectorially tothe vector Ex at right angles thereto. 'I'he resultant triangle ofvoltage vectors Vshown in dotted lines in Fig. 2 connecting points 2,Ya, Yi is the voltage vector compensated for both resistance drop andreactance drops in the circuit that is applied to the regulator voltageresponsive element through the rectifying elements 34, 35 and 33. Theseveral parts of the circuit across which voltage components aredeveloped, are connected so that the voltage vectors add or subtract inthe manner shown in Fig. 2.

It will be apparent from the above descrip-V tion of apparatus andcircuits that a voltage has been developed from a single phase currentwhich calli be added to, or subtracted from, the three-phase voltage ofthe local circuit I', 2' and 3 through which the voltage responsivedevice I3 is energized from the main power circuit I, 2 and 3 to producea balanced compensated three-phase voltage.

Many modifications of the circuit and apparatus illustrated anddescribed within the spirit of my invention will occur to those skilledin the art, and I do not wish to Ibe limited otherwise than by the scopeof the appended claims.

I claim as my invention:

1. In combination, a three-phase electric power circuit, a deviceresponsive to a three-phase voltage, a three-phase local circuit forsupplying voltage to said device that is a measure oi the voltage of thepower circuit, means for compensating the voltage applied to saidvoltage responsive device for the voltage drop in said power circuitcomprising a winding to which a voltage is applied that is a measure ofthe current in one power circuit phase conductor, a network connected tosaid winding for developing voltage components having predeterminedphase relationships to two phase voltages, said network includingreactor and resistor elements connected in series across said winding,and means for introducing voltage components developed across theseelements into two circuit conductors of the three phase local circuit.

2. In combination, a three-phase electric power circuit. a deviceresponsive to a three-phase voltage, a three-phase local circuit forsupplying voltage to said device that is a measure of the voltage of thepower circuit, means for compensating the voltage applied to saidvoltage responsive device for the voltage drop in said power circuitcomprising a winding to which a voltage is applied that is a measure ofthe current in one power circuit phase conductor, a network connected tosaid winding for developing voltage componentsy having predeterminedphase relationships to two phase voltages, said network includingreactor and resistor elements connected in series across i said winding,and means for introducing voltage components developed across theseelements into two circuit conductors of the three phase local circuitthat are in phase with the ohmic drop in the respective phases of thepower circuit.

3. In combination, a three-phase electric power circuit, a deviceresponsive to a three-phase voltage, `a three-phase local circuit forsupplying voltage to said device that is a measure of the voltage of thepower circuit, means for compensating the voltage applied to saidvoltage responsive device for the voltage drop in said power circuitcomprising a winding to which a voltage is applied that is a measure ofthe current in one power circuit phase conductor, a network connected tosaid winding for developing voltage components having predeterminedphase relationships to two phase voltages, said network includingreactor and resistor elements connected 4in series across said winding,andmeans for introducing voltage components developed across theseelements into two circuit conductors of the three phase local circuitthat are in phase with the reactive drop in the respective phases of thepower circuit.

4. In combination, a three phase electric power circuit, a deviceresponsive to a three-phase voltage, a three-phase local circuit forsupplying voltage to said device that is a measure of the voltage of thepower circuit, means for compensating the voltage applied to saidvoltage responsive device for the voltage drop in said power circuitcomprising two compensating devices each having a three phase voltagesof the power circuit, said network including reactor elements andresistor elements connected in series across the winding, and means forintroducing voltage components developed across these elements into twocircuit conductors of the three phase local circuit to compensate forohmic voltage drop and reactive voltage drop in the power circuit.

5. In combination, a three phase electric `power circuit, a deviceresponsive to a three-phase voltage, a three-phase local circuit forsupplying voltage to said device that is a measure of the voltage of thepower circuit, means for compensating the voltage applied to saidvoltage responsive device for the voltage drop in said power circuitcomprising two compensating devices each having a winding to which avoltage is applied that is a two circuit conductors of'the localcircuit, one

of said networks including a plurality of resistor elements and areactor element for developing voltage components that are in phase withthe reactive drop in two phases of the power circuit, and means forintroducing said components into two circuit conductors of the localcircuit to produce a balanced three phase compensated voltage.

6. In combination, a three-phase electric power circuit, a deviceresponsive to a three-phase voltage, a three-phase local circuit forsupplying voltage to said device that is a measure of the voltage of thepower circuit, means for compensating the voltage applied to saidvoltage responsive device for the voltage drop in said power circuitcomprising two compensating devices each having a Winding to which avoltage is applied that is a measure of the current in one power circuitphase conductor, a network connected to each of said windings fordeveloping voltage components having predetermined phase relationshipsto the three phase voltages of the power circuit, one of said networksincluding a plurality of resistor elements and a reactor element fordeveloping voltage components that are in phase with the reactive dropin two phases of the power circuit, and means for introducing saidcomponents into two circuit conductors of the local circuit to produce abalanced three-phase compensated voltage.

7. In combination, a three-phase electric power circuit, a deviceresponsive to a three-phase voltage, a three-phase local circuit forsupplying voltage to said device that is a measure of the voltage of thepower circuit, means for compensating the voltage applied to saidvoltage responsive device for the voltage drop in said power circuitcomprising two compensating devices each having a winding to which avoltage is applied that is a measure of the current in one power circuitphase conductor, a network connected to each of said windings fordeveloping voltage components hav-V ing predetermined phaserelationships to the three phase voltages of the power circuit, one ofsaid networks including a plurality of reactor elements and a resistorelement for developing voltage components that are in phase with theohmic drop in two phases of the power circuit, and means for introducingsaid components into `,two circuit conductors of the local circuit toproduce a balanced threephase compensated voltage.

LAWRENCE L. FOUNTAIN.

